Iminophosphorane-substituted proton sponges. Part 5. Structures in the solid state. Correlation between solid state³¹P MAS NMR spectra and crystal structures

Abstract

The 31P N M R spectra of protonated iminophosphorane-substituted proton sponges of k n o w n crystal structure have been recorded in the solid state under the conditions of magic angle spinning (MAS) and 'H-decoupling. Variable temperature experiments and a comparison with the averaged 31P chemical shifts in solution show that no proton transfer occurs in the crystal, even when strong intramolecular hydrogen bonds are present. Good agreement between the N M R results and the X-ray structures gives weight to structural predictions based on solid state 31P MAS NMR spectroscopy, for compounds which do not yield suitable monocrystals.

Selective Metal‐Cation Recognition by [2.2]Ferrocenophanes: The Cases of Zinc‐ and Lithium‐Sensing

“…In addition, the shift experienced by the ipso-carbon atom of the aromatic rings is in excellent agreement with those found in the conversion of an iminophosphorane unit into the corresponding aminophosphonium salt. [21] These spectroscopic results confirm that the complexation of the Li + cations by the receptor 4 gives rise to an increase in the rate of the conformational equilibrium, as is shown by the simultaneous increase in the resolution of the spectra upon addition of Li + . A shifting of the peaks was observed in all the NMR experiments, which indicates a fast equilibrium between complexed and uncomplexed species compared with the acquisition times of these techniques.…”

A review with comprehensive data on experimental indirect scalar NMR spin–spin coupling constants across hydrogen bonds

“…In as early as 1993, [93,94] some of us reported a 4h J PP coupling constant in compound 77 (Scheme 30). It was estimated at about 3 Hz but a later study using different NMR fields allowed us to measure it precisely as 1.6 Hz.…”

Bi-functional and mono-component organocatalysts for the ring-opening alternating co-polymerisation of anhydride and epoxide

“…As reported in the table in Scheme 2, the 31 P chemical shifts are calculated to be 11 ppm for the neutral monomeric species and 25 ppm for a neutral dimeric species reproducing nicely the experimental findings. The 31 P chemical shift of the neutral monomeric species is higher than the 31 P chemical shift of a mono-functional neutral iminophosphorane (δ31 P = 3 ppm), 38 which indicates hydrogen bonding 39 between the iminophosphorane's nitrogen and the urea moiety, as confirmed by the optimized DFT structure (cf. ESI, † Fig.…”